Research
Below are my main current projects, collaborations and a list of opportunities to join the group.
There is also a separate, dedicated page for past projects and results.
Current projects
Understanding turbulent transport processes in the coastal ocean
​Humans are largely a coastal species, with most of Britain’s population and 40% of the world’s population living within 100 km of the coast. Estuaries are particularly important, being vital transition and exchange zones between rivers and the sea and often hosting great cities like London. Rising sea levels, pollution, and population growth threaten these regions and their essential services. Fresh water will likely become the "gold" of the 21st century, central to health, industry and increasingly scarce. Ocean turbulence drives the transport of salt, pollutants, sediments and nutrients affecting water quality, erosion, fisheries, and infrastructure like wind turbines and subsea pipelines and communication cables. Turbulence remains one of the last unsolved problems in classical physics, and better understanding how it mixes stratified water layers is key to environmental engineering efforts for climate change mitigation. My research tackles this challenge by combining cutting-edge field observations, lab experiments, and computer simulations that probe turbulence in unprecedented detail.
Collaborations: A. Mashayek, A. Atoufi (U. Cambridge, Earth Sciences) and others through the Ocean Turbulence Special Interest Group.
Revealing shear instabilities in estuaries with multibeam sonar imagery
In most of the ocean, including estuaries, denser water layers lie below lighter ones. In such stably-stratified systems, turbulence is often initiated by shear instabilities triggered by tidal forces or underwater topography. Instability grows into a beautiful coherent wave structure, as visualised above by sonar from an autonomous underwater vehicle in the Connecticut River estuary. This growing underwater wave then breaks into disorganised turbulence, mixing the layers. We are currently analysing game-changing multi-beam sonar imagery of turbulent mixing from US collaborators. These data show that mixing does not always occur by breaking in the ‘cores’ of the wave on a scale of 1 m (seen above), but also by smaller secondary shear instabilities along the ‘braids’ on a cm scale (see yellow regions above, ignoring the bright fish!) These findings provide new insights into the turbulent 'energy cascade' from large to small scales controlling the mixing rates of salt, nutrients, dissolved gasses, etc.
Collaborations: W. R. Geyer (Woods Hole Oceanographic Institution), C. Bassett (U. Washington)
Measuring stratified turbulence in the lab with high-speed laser and cameras
To complement direct observations, laboratory experiments are crucial, like the Stratified Inclined Duct (SID, pictured above)​. This experiment, which I developed at Cambridge, uniquely sustains geophysically-relevant stratified turbulence under more controlled conditions than in the field. It also allows us to measure the flow with much higher resolution and accuracy using fast lasers and cameras to perform simultaneous, 3D Particle Image Velocimetry and Laser Induced Fluorescence. These data led to breakthroughs on the energetics of sustained stratified mixing and 3D coherent structures (see past projects). We are now extrapolating these findings from the laboratory scale to the geophysical scale using theory and models developed in tandem with observations (see above) and simulations (see below). Imaging stronger and faster turbulence with higher-speed laser and cameras (up to 1 kHz) would be an exciting research frontier to pursue for a gifted and ambitious PhD or postdoc!
Collaborations: S. B. Dalziel, P. F. Linden (U. Cambridge, DAMTP), X. Jiang (Imperial College, Aeronautics)
Probing the finest scales of mixing with exascale simulations on GPU clusters
Computational fluid dynamics is a precious tool to complement field observations and laboratory experiments and build better models of turbulence. To do this, we must solve (but only approximately!) the 200-year-old Navier-Stokes equations governing turbulence on massive grids because of the extreme range of scales involved. This is particularly challenging in stratified turbulence, because energy cascades down to very small (micrometre) scales where the mixing of salt, heat or other tracers occurs. The ground-breaking simulations that we are currently analysing (pictured above) faithfully reproduce for the first time, the same kind of mean-shear-forced turbulence observed in the above estuary and lab experiment. These simulations were pioneered and run by collaborators in the USA on the world's first exascale computer, Frontier. They involved tens of thousands of GPUs, performing in parallel several billion billion operations per second (exaFLOPS), and are also quite challenging to analyse...
Collaborations: M. Couchman (York U. Toronto), S. de Bruyn Kops (U. Massachusetts Amherst) and others in the STRATA group: Supercomputing for Stratified Turbulence Research Advancing Theory and Applications.
Group
We are looking for students and postdocs to join the group. Please get in touch if the above research sounds exciting and you have a strong quantitative background (engineering, physics, mathematics or similar degree).
PhD opportunities
Funded project:
Exploring stratified turbulent mixing by shear instabilities in coastal waters
​See the full advert here with instructions on how to apply for a start in 2025.
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Other sources of funding:
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A number of competitive scholarships are available from Imperial College and the Department of Civil and Environmental Engineering, with various eligibility criteria (start in 2025 still possible)
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Scholarships are available from the Mathematics for our Future Climate: Theory, Data and Simulation (MFC) Centre for Doctoral Training (CDT) for a start in 2026.
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Eligible students may consider the Commonwealth PhD scholarship.
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External scholarships from foreign governments or private foundations also exist, such as the Chinese Government Scholarships or the Croucher Scholarship (Hong Kong).
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For more information, see Imperial's comprehensive 'Scholarships' page, and its search engine.
Postdoctoral opportunities
Researchers interested to join my group for a postdoc can apply to a range of fellowships:
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Royal Society International Newton Fellowship (including the K C Wong Fellowships for Chinese applicants)
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Royal Commission for the Exhibition of 1851 Research Fellowship
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Swiss National Science Foundation 'Postdoc.Mobility' for applicants from Switzerland
... and probably many others. Note that each scheme has a particular set of eligibility criteria.
Previous group members
2025
Jake Hewison from University of Cambridge (MMath Mathematics)
“Do fish mix the ocean?” (experiments)
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2024
Valentin Samson from École Polytechnique (MSc Engineering)
“Direct numerical simulations of stratified turbulence” (numerics)
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Daniel Ward from University of Cambridge (MMath Mathematics)
“The transitions to turbulence viewed through the lens of laboratory experiments” (essay)
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2023
Marvil Cheung from University of Cambridge (MMath Mathematics)
“Reduced-order modelling of intermittency in stratified turbulence” (numerics)
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2022
Arianna Cox from University of Cambridge (Mathematics)
“Machine learning to the rescue of big data: classifying experimental stratified turbulence” (numerics)
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Stasiu Wolanski from University of Cambridge (BA Physics)
“High-speed, high-resolution imaging of early bubble growth in decompressed hydrogels” (experiments)
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Jason Tang from University of Cambridge (BA Mathematics)
“Modelling of the transition from elastic cavity to fracturing crack in decompressed hydrogels” (modelling)
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Keshav Raghavan from University of Cambridge (MMath Mathematics)
“Data assimilation and super-resolution reconstruction of experimental turbulent flows” (essay)
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2021
Aly Kombargi from Ecole Polytechnique (MSc Engineering)
“Early-stage growth of gas-filled cavities in decompressed hydrogels” (experiments)
2020
Yansheng Zhang from University of Cambridge (BA Physics)
“Giving hydrogels the bends: experiments” (experiments and modelling)
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Zhiyuan Wei from University of Cambridge (BA Physics)
“Elastic modelling of spherical and fracturing bubbles in soft brittle solids” (modelling)
Joshua Cudby from the University of Cambridge (BA Mathematics)
“Weakly nonlinear Holmboe waves” (theory & numerics)
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2018
Yves-Marie Ducimetière from EPFL (MSc Engineering)
“The effects of confinement in stratified shear flows” (theory & numerics)
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2017
Ling Qu from South China Sea Institute of Oceanology in Guangzhou, China (PhD visitor)
“Experiments on buoyancy transport in a stratified inclined duct” (experiments)
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